Paper II · Part B — Physics

Sound Waves and Musical Instruments

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Build exam-ready understanding by connecting the core idea, formulas or facts, worked example and previous NDA questions. Focus on why each rule works, then test it under timed conditions.

Concept

Sound is a longitudinal mechanical wave that needs a medium to travel. Its pitch depends on frequency and loudness on amplitude. Echoes arise from reflection of sound.

Sound travels fastest in solids and cannot travel through a vacuum.

Key Points & Formulas

Sound speed: solids > liquids > gases; ≈ 343 m/s in air.
Pitch ↔ frequency; loudness ↔ amplitude.
Audible range for humans: 20 Hz to 20,000 Hz.
Echo: reflection of sound from a distant surface.

Worked Example

Q. Why can sound not travel through a vacuum?

Sound is a mechanical wave that needs particles to vibrate.

A vacuum has no medium/particles.

Hence sound cannot propagate through it (unlike light).

Common traps

Reading the prompt too quickly and missing a qualifier.
Memorising the result without checking when it applies.
Skipping units, signs, chronology or the final reasonableness check.

NDA shortcuts

State the governing rule before substituting values.
Eliminate impossible options before doing full calculation.

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Past-paper bank

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5 NDA questions

Choose an answer before the solution appears. Option order is mixed automatically.

Question 1

NDA Practice 2026

An echo is produced due to the ____ of sound.

Question 2

NDA I 2025

The frequency (f), wavelength (λ) and speed (v) of a sound wave are related as

Question 3

NDA I 2024

Which one of the following does not apply to sound waves in fluids?

Question 4

NDA I 2024

Consider the two statements given below:
Statement-1: Infrared waves are also called heat waves.
Statement-2: Water molecules readily absorb infrared waves.
Select the correct answer using the code given below:

Question 5

NDA I 2023

Which one of the following statements is NOT true for a flute, a musical instrument?

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